191 



also inarlv»^(I, the Liotlioidib beiiijx iiiiich less dependent upon their hosts 

 than the IMiilopteiidje. Most ot them tiiivel freely and live for some 

 time away from their hosts, while the Philopteridje cling- fast to the 

 host even after its death. In both <iToni)s, however, we have special 

 structures resultinji' from their enviromiieut, such as the palettes upon 

 the basal joint in L;i!mobothrium and alUed genera, and ridged or ser- 

 rated surfaces, to add to the rigidity of hold. 



In Pediculidie the tarsal sti'ucture presents some remarkable resem- 

 blances to that of Philoi)teridie in the large basal joint and more slen- 

 der claw-bearing joint. Special roughened, serrated, or ridged siu'faces 

 are also common on the second joint, and the claw is often serrated or 

 roughened on the inner face. A peculiar structure which I have de- 

 scribed in H(vmi(topinas suis* consists of an extensible pad at the end 

 of the tibia, which is so located as by its extension to press upon the 

 hair surrounded by the claw, and would seem a most useful organ in 

 strengthening the hold upon the hair and adapting the clasping struc- 

 ture to variations in the diameter of the hair at different points. In 

 some species the claw becomes flattened into a nail-like organ, and a 

 certain amount of rotation of tibial i)arts is observed. 



Reviewing now hastily the characters which have been sketehed and, 

 ' I think, that for the Mallophaga, with the exception of wings, the loss of 

 which has been stated as occurring before the assumption of the para- 

 sitic habit, we must admit that parasitism has resulted in specialization 

 and progressive evolution, not retrogression or degradation. The 

 short antennie of Ave or three joints present certainly as high a degree 

 of development as the fifteen-jointed but simple antennae of their free 

 relations. The tarsi and claws present in every case specialization, and 

 in some cases development of highly organized modifications of the 

 simple feet. The mouth parts show specialization of mandibles and 

 reduction, it is true, in labial and maxillar structure, but very little re- 

 duction from the Psocid type, and a reduction that need not be looked 

 upon as rendering them inferior in any way in the use of these parts 

 or the purposes to which they may be put. 



It seems to me, therefore, that while in many cases parasitism un- 

 doubtedly results in degradation, the results, excepting for wings, in 

 these insects have been specialization without degradation. It would 

 seem more proper to consider that we have specialization of those organs 

 the use of which is retain«'d, and degradation in organs that fall into 

 <lisuse, while the (piite common expression that parasitism entails de- 

 gradation appears to me to be in this respect somewhat inexact. 



" Bull. 7, Div. Entomology U. S. Dept. Agriculture, p. 20. 

 12201— Xo. r> .3 



